Electrolytic development of a subtractive color-forming photoconductive member



ELECTROLYTIC DEVELOPMENT OF A SUBTRACTIVE COLOR-FORMING PHOTOGONDUCTIVE MEMBER Filed Oct. 9, 1963 July 4, 1967 E. E. RENFREW 3,329,590

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Array/v57? United States Patent 3,329,590 ELECTROLYTIC DEVELOPMENT OF A SUB- TRACTIVE COLOR-FORMIN G PHOTOCON- DUCTIVE MEMBER Edgar Earl Renfrew, White Bear Lake, Minn., assignor to Minnesota Mining and Manufacturing Company, St. Paul, Minn, a corporation of Delaware Filed Oct. 9, 1963, Ser. No. 314,941 3 Claims. (Cl. 204-18) This invention relates to a reproduction process. In another aspect this invention relates to a novel graphic reproduction receptor. In still another aspect this invention relates to a process and a copy sheet for the reproduction in color of colored images and patterns.

Basically, there are two types of color reproduction processes; the additive color process and the subtractive color process. The Findlay process and the Dufay process are examples of additive color processes. In the Findlay process a very fine mosaic (checkerboard) filter consisting of red, green, and blue elements (the three basic colors necessary for color reproduction) is printed on a glass plate. This is placed in direct contact with a panchromatic silver halide emulsion layer on glass. The color picture is exposed through the mosaic filter onto the silver halide layer. The filter is then taken away and the photographic plate processed by reversal technique to yield a positive image. When the finished plate is held in register with the mosaic filter and viewed by transmitted white light, a color picture is observed. The operation of the system is briefly as follows: In a red area of the picture, light will pass only through the red elements of the mosaic and the film will be exposed only in these areas. On developing by reversal technique, these areas become clear and the unexposed areas behind the green and blue elements become black. Thus, when the filters are put back in place, the red elements are over clear spots and the blue and green elements over black spots and only red light can be seen on viewing through in this area. The intensity of the red light making the exposure of the silver halide layer controls the degree to which it will develop (by reversal) to a clear area. Thus, the tone of the red is controlled and properly reproduced. Similar reasoning holds for the green and blue filters. Since all the filter elements are extremely small, the picture viewed by transmitted light looks like a full color picture in hue and tone.

The Dufay process is essentially the same as the Findlay process except that the color mosaic is printed with colored lacquers on film stock and the silver halide emulsion is coated directly on the colored film. This solves the problem of registering the filter with the developed image for viewing.

These two processes are suitable only for viewing by transmitted light of high intensity, since in an area of a given color, two-thirds of that area must be blacked out to hide the unwanted colors. These processes are not useful with opaque (paper) stock where the reproduction must be viewed by reflected light.

The most successful of the photographic color processes have been those based on the subtractive tripack. The tri-pack consists of three layers coated one cyan dye but has no effect on the dyes of the other two layers. When red light falls on the subtractive tri-pack, the cyan is removed and a red color results. By exactly the same process green light destroys the magenta dye and leaves a green color (the cyan and yellow layers viewed subtractively). Similarly, blue light destroys the yellow layer and blue is produced.

The above technique is used in the Gaspar (or dye bleach) process of color photography. In this process, the cyan colored layer contains in it a silver halide emulsion which is selectively sensitive to red light and a cyan colored dye. The magenta layer contains in it a silver halide emulsion which is sensitive only to green light and a magenta colored dye, and the yellow layer is sensitive only to blue light and contains a yellow dye. The three layers, one over the other, look essentially black. When a positive color picture is projected on this black sheet, the red portions affect the silver halide emulsion in the cyan layer only; the green portions the magenta layer; and the blue portions the yellow layer. The exposed tri-pack is next developed and fixed as an ordinary silver halide type of sheet. In the cyan layer, silver metal is produced in proportion to the red image; in the magenta layer silver is produced in proportion to the green image; and in the yellow layer, in proportion to the blue image.

The sheet is next placed in an acid thiourea solution containing a catalyst. In this solution the silver metal causes the reduction of (bleaching of) the dyes in proportion to the amount of silver metal present in each layer. Lastly, the silver salts and any remaining free silver are dissolved out; the print washed and dried. The result is a full-colored, positive picture produced by the subtractive effect of light going through the three layers and reflecting back off the white paper on which they are coated.

All modern color processes are variations of the subtractive tri-p-ack. In the well known Ektachrome positive film, the dyes are formed chemically rather than by being bleached away or destroyed. In the three layers are essentially the three silver halide emulsions selectively sensitive each to one of blue, green, or red light. There is also present in the blue sensitive layer a relatively colorless chemical which will later produce a yellow color. Similar arrangements are made in each of the other layers to produce in later development magenta and cyan. The first development step utilizes silver developer which uses up silver halide in the exposed areas in each layer (converts it to silver) in proportion to the blue, green, and red exposures, respectively. After the first development step, unused silver halide is now present in proportion to the positive image of each color. The film is then flooded with white light to expose all the remaining silver halide, and this is then developed with a special developer which as it forms silver metal from silver halide changes to a compound which in turn reacts with the other special chemicals in each layer to produce yellow, magenta, and cyan, respectively, in proportion to the positive images. The silver metal present is next chemically removed and the film washed and dried.

The present process and reproduction receptor overcomes the disadvantages of the above techniques for color reproduction in that the present invention is not limited to type of receptor, is unusually simple, and requires only a simple development stage. In essence, the present invention is a combination of the subtractive color technique with photoconductive materials as the radiation responsive element rather than silver halide type materials.

An object of this invention is to provide a new reproduction process.

Another object of this invention is to provide a new and useful reproduction receptor or copy sheet.

Still another object is to provide a simple development technique for developing a reproduction in color.

Yet another object is to provide new color responsive combinations of materials.

A further object of this invention is to provide a subtractive color process having superior color rendition and contrast as compared to an additive color process.

Yet another object is to provide new color forming combinations for photoconductors.

Various other objects and advantages will become apparent to those skilled in the art from the accompanying description and disclosure.

In accordance with this invention, a photoconductive receptor is utilized as the radiation responsive element of the invention. This photoconductive receptor comprises an electrically conductive substrate or support upon which has been deposited a photoconductor, which photoconductor renders the receptor responsive to radiation such as light, whereby light-struck areas are rendered more conductive than the non-light-struck areas. The receptor is exposed to a colored light image or pattern. The result is that a differentially conductive pattern is formed upon the receptor corresponding to the image or pattern to be reproduced. Instead of using a photoresponsive layer on the receptor which is uniformlyl responsive to the same wave lengths, the photoconductive layer of the receptor of this invention is divided into a multiplicity of three selectively light responsive photoconductive areas. These three selectively light responsive areas, which are placed laterally rather than overlying each other on the sheet, are respectively photoconductively responsive selectively to blue, green and red light. These selectively light responsive areas may be placed upon the photoconductive receptor in the form of a pattern of dots, spheres, circles, beads, pyramids, squares, triangles, hexagons, lines, narrow bands and stripes, etc. For example, in the case of a selectively light responsive pattern in the form of lines, one line is selectively photoconductively responsive substantially only to blue light. The next adjacent line is selectively photoconductively responsive substantially only to green light, and the next line is selectively photoconductively responsive substantially only to red light. These three line patterns are successively repeated across the surface of the receptor. In the case of dots, beads or geometrical areas, the three areas are in the form of a mosaic or pattern of repeating combinations of the three selectively responsive areas. For example, a repeating successive series of three differently colored dots or squares are placed in the form of a row across the surface of the receptor. The three differently colored dots are selectively photoconductively responsive, respectively, to blue, green and red light. Similar rows of dots are placed adjacent the first row to form a pattern of many rows and the dots are similarly selectively responsive to blue, green and red light; but, preferably, the dots or squares are staggered in respect to the preceding row so that two dots or squares selectively responsive to the same color are not directly adjacent to each other. Even a random mosaic of the three selectively light-sensitive photoconductive areas may be utilized with success. Each of the ditferent light-sensitive photoconductive areas are made up of a suitable photoconductor, such as zinc oxide, which is sensitized with a different dye or other organic material to make that particular area selectively light responsive to only one of the colors, blue, green and red. In addition to the photoconductor and colored light responsive sensitizer, each of the three successive areas contains a different organic chemical compound or unreacted mixture of chemical compounds capable of giving that area a specific subtractive color when subsequently developed. The blue sensitized areas are capable of producing a visual yellow color on development. The green sensitized areas are similarly capable of producing the color magenta, and the red sensitized areas are capable of producing the color cyan. The amounts of dyes or other organic materials utilized for imparting to the photoconductor its particular colored ligh response is such that a white photoconductor is not substantially colored although in the same instance a slight tint may be observed.

As a typical method for preparing such a pattern or mosaic, the ingredients of the composition forming a specific area of the mosaic or pattern (including photoconductor, color producing chemical or chemicals, sensitizer, etc.) are mixed with a suitable organic insulating resinous binder, such as Pliolite (a copolymer of butadiene and styrene), and a small amount of solvent, such as toluene, to form a dispersion of the photoconductor in a solution of the organic chemicals. Three different dispersions are thus prepared and are then applied in a definite or random pattern, in the form as previously discussed, to the surface of the receptor. The solvent evaporates and the binder afiixes the photoconductor and chemicals to the receptor surface. The support or substrate for the photoconductor is electrically conductive, such as a metal plate, film or foil or a metal film bonded to the surface of a sheet of plastic, wood pulp paper, cloth, wood, etc. Preferably, for making color reproductions or prints the substrate is rnetallized paper or plastic film. The appearance of the completed receptor is a flat substantially white or colorless surface. Preferably the selectively sensitive dots and lines are about 0.001 to about 0.01 inch in width or diameter.

Upon exposure to a colored light image or pattern, the yellow producing areas become conductive where struck by blue light; the magenta producing areas become conductive where struck by green light; and the cyan producing areas become conductive where struck by red light. Exposure may be effected in a conventional manner, such as by the projection of a colored image from a color positive onto the surface of the receptor by means of a con ventional transparency projector and lamp, for a period of time between about 0.001 second and about one minute. Exposure may also be effected with a camera and lens focused on a lighted subject. Successive exposure through conventional blue, green and red filters enhances the selectivity of the receptor to the respective colors.

Having been exposed to the color image or pattern, the receptor is differentially conductive in a latent pattern corresponding in intensity and tone to the original color image and is ready for development which includes a plurality of steps. Development, at least in part, may be effected either simultaneously with or subsequent to the exposure step. The first development step involves the imagewise coating or deposition of a white opaque material such as a white pigmented resin, over the conductive areas by electrolysis as will hereinafter be discussed in detail. In other words, the white opaque material is deposited on all of the light-struck areas sensitive to red, green or blue in proportion to the tone, intensity and hue of the original color. In a modification of this first step, instead of depositing a white opaque material on the conductive area the color in the conductive area may be rendered inert to subsequent steps of development, such as by decomposing the active chemical or chemicals or reacting the color producing chemical with another chemical the product of which is inert and colorless or white. In any event, the first step of the development, in essence, comprises blocking out the conductive areas to subsequent development steps regardless of the particular color to which each area is responsive.

The result on the receptor is that in an overall area which has been struck by red light, the only active color producing areas remaining are the subtractive colors, yellow and magenta. In an overall area struck by green light, the only active color producing areas remaining are yellow and cyan. In an overall area struck by the blue light, the only active color producing areas remaining are magenta and cyan. Since the active color forming chemicals re maining are subtractive, the visual additive effect of such colors, when chemically developed, will be the desired primary color.

The drawing diagrammatically illustrates a portion of receptor sheet greatly enlarged. FIGURE 1 is an illustration of the mosaic or pattern of potential subtractive colors of a photoconductive sheet. FIGURE 2 illustrates the receptor after the electrolytic development step and FIGURE 3 represents the same sheet after the chemical development step.

The chemical development of the color producing areas depend upon the type of color producing chemicals used. These color producing chemicals and the method of chemical development associated therewith can be classified into two generally recognized color producing systems, namely; (A) azo system; and (B) oxidation system, which systems are described generally below:

(A) AZO SYSTEM heat and/or Coupler diazonium developer azo dye pH change In one embodiment of the azo system a colorless coupler is incorporated into a white photoconductive coating, together with a sensitizing material. Thus, as shown in FIGURE 1 of the drawing, in a three-color system, mosaic or otherwise separated areas (C Y and M would contain different couplers. The capital letters represent couplers which yield on chemical development, respectively, cyan, yellow and magenta dyes. The subscripts indicate the light to which the respective areas are responsive, namely, red, blue and green. Thus, C is a cyan producing area and contains a sensitizer enhancing response for red light. Preparation of the receptor, dark adapting and exposure to a multicolored image, as from a color slide, is carried out as described. Electrolytic placing of a white pigmented resin is carried out, and the electrolytically treated receptor is heated, if need be, to fix the resin to the receptor. Then a solution of a developer is spread over the entire receptor and the receptor permitted to dry, leaving a layer of the developer uniformly coating the entire receptor. In the case of reaction (1) above in which a developer base is used, the exposed and treated sheet is then painted, sprayed, or bathed with an aqueous solution of sodium nitrite to which has been added a small amount of an acid; diazotization of the developer and coupling with the coupler occur, producing a visible colored dye or pigment. In the case of reaction (2) above in which a diazonium developer is used, heat, either alone or in the presence of certain acids, bases or catalytic materials brings about the production of colored products.

Thus, if red light hits a red sensitive area C, of the mosaic, conduction will take place in that area, and the area so exposed will be eifectively covered by the resinous material when electrolysis is carried out in an aqueous emulsion or solution of the resin as shown in FIGURE 2 of the drawing. In this area C becomes covered, and no cyan dye can be formed. However, the neighboring areas are not affected by the red light, and the coupler of Y5 reacts with a diazotized base to yield the visual color yellow, and the coupler of M reacts with a diazotized base to give the visual color magenta. The effect of magenta and yellow is, of course, red when integrated by the eye or when mixed together by a solvent as shown in FIGURE 3 of the drawings.

Similarly, an area activated by green light after electrolysis will be unable to furnish any color from the area M and the effect in the overall area will be to produce cyan and yellow together, yielding the desired effect, green. Blue light brings about the blocking of the area Y which is sensitized to it. The remaining M and C areas yield on chemical development magneta and cyan, which seen together give visually blue.

In another embodiment of the azo system both the coupler and developer chemical are incorporated into the mosaic or pattern of the photoconductive coating; each selective area of the mosaic having the appropriate combination of chemicals to give the desired subtractive color on chemical development. In this embodiment, the first development step as in the previous embodiment is the electrolytically placing of a white pigmented resin on the receptor in selected areas as described. Thereafter, only one step of chemical development is required; namely treatment of the receptor with an aqueous solution of nitrous acid when the developer chemical is a developer base or with heat or change of pH when the developer chemical is a diazonium developer. In this embodiment, the developer chemical should be substantially white or colorless and should be sufiiciently stable not to react with the coupler under the environment of storage and bandling of the receptor.

(B) OXIDATION SYSTEM Selected colorless couplers (which may be but are not necessarily similar to or related to those of the azo system) are included in the coatings which are placed in the desired areas, Y C and M of a mosaic pattern together with their proper sensitizers. Exposure and electrolyzing the exposed receptor in an aqueous resin system is done similarly to the azo method. An appropriate chemical developer for this system is then applied and the receptor dried. Oxidation by an oxidizing agent which is applied to the surface brings about the production of the desired colors in the desired areas in a manner analogous to the azo system. As in the azo system, both the coupler and chemical developer can be incorporated into the mosaic of the photoconductive coating. The chemical development step then involves only the application to the surface of the receptor of the oxidizing agent. In this latter case as with the azo system the developer should be white or colorless and sufiiciently stable.

The receptor of the present invention is an electrically conductive sheet containing a continuous metal layer. The metal layer may itself be suflicient as a self-supporting layer for the photoconductive layer of the receptor or may be bonded or aflixed to a backing for support or insulation purposes. Foils or films of metal are suitable as a selfsupporting metal layer. When a. backing is utilized, the metal is deposited upon the backing or adhered thereto in the form of a continuos film or foil. The metal layer can be deposited on the backing by vapor deposition, electro-plating, precipitation, lamination of metal foil, or by bonding metal particles thereto with a suitable binder. Conductance of the metal layer is important since the metal layer is used as the conductor to one of the electrodes of the direct current source during the electrolytic development step. Therefore, the metal layer should offer no more lateral or surface resistance than about 1,000 ohms, preferably no more than 10 ohms, per square. The thickness of the metal layer, of course, will depend upon whether it is the support itself or whether it is utilized merely as the conductor. When the metal layer is utilized upon a nonconductive backing, the thickness of the metal layer is usually between about 0.1 and about 25 microns. Suitable backing material for this metal layer is wood pulp paper, rag content paper, glass, and plastic films, such as cellulose acetate films, Mylar films, polyethylene films and polypropylene films. Even cotton or wool cloth may be utilized as the backing without departing from the scope of this invention. Suitable metals for the metal layer include aluminum, tin, magnesium, chromium, silver and copper; preferably aluminum.

As previously indicated, the response of the receptor to the radiation pattern or light image is accomplished with the use of a suitable photoconductor. Numerous known photoconductors may be utilized for this purpose, both organic, such as anthracene, and inorganic, such as selenium. Preferably these photoconductors are inorganic and substantially insoluble in the solvents and chemicals utilized. Usually, the inorganic photoconductors are utilized in particulate form as a very fine powder and are preferably white or light colored. Generally, the average diameter of the photoconductor particle is between about 0.1 and about 1 micron. Preferred inorganic photoconductors include zinc oxide, indium oxide, cadmium sulfide, lead sulfide and mercuric oxide.

Since photoconductors vary considerably in their photoconductivity upon exposure to light and also in their resistivity in the dark, the particular photoconductors to be utilized will depend to some extent upon the type of electrolytic development procedure to be employed e.g. anodic or cathodic. Also for electrolytic development of the colored image, the photoconductor should have a relatively high conductivity upon exposure to light since a minimum resistance exhibited by the photoconductor is desirable for electrolytic development. In general, for electrolysis the photoconductor must have a photoconductivity or conductivity upon exposure to light of at least mho/ cm. (measured in an electrolytic cell with an 0.8 mil zinc oxide coating and extrapolated to a cubic centimeter). The dark conductivity (dark adapted conditions) of such a photoconductor will be 10 to 100 times less or even less than the conductivity in the light. When particulate photoconductors are used the photoconductor particles should be substantially in direct contact with each other as well as with the electrically conductive portion of the support or the substrate, such as the metal layer, in order to provide the minimum of resistance to current passage between particles and substrate.

As previously stated, dyes and organic chemicals are utilized in combination with the photoconductor as selective colored light sensitizers and as potential colorants for the mosaic surface areas. In general, the dyes in the quantity used color the surface or particle of photoconductor only very slightly. No binder or resin is needed to hold the dye to the surface of the photoconductor. These dyes and chemicals should be such that there is substantially no chemical reaction between the dye and the photoconductor which would interfere materially with the photoconductive properties of the photoconductor. In addition, the dyes and chemicals should be capable of being bonded to the photoconductor in some manner. For example, bonding may be achieved between the dye or chemical and photoconductor by ligand formation, by adsorption, or by chemical bonding, which type of bonding is inherent in the dye or chemical itself.

Selective colored light sensitizing dyes or other organic materials for photoconductors are known in the art. Suitable dyes capable of selectively sensitizing the photoconductor, such as zinc oxide, to red light include the triphenylmethane dyes, Patent Blue V (CI. 42045), Victoria Blue B (CI. 44045), Xylene Cyanole FF (C.I. 42135), Alphazurine 2 G (C.I. 42045), and Ponta-cyl Brilliant Blue A (CI. 42080). Suitable dyes for selectively sensitizing the photoconductor to green light include the xanthene dyes, Pyronine B (C.I. 45010), Phloxine B (CI. 45410), Rhodamine G (C.I. 45150), Rhodamine B Base (CI. 45170). and Violamine (C.I. 45190); the azine dyes, Methylene Violet (C.I. 50205) and Neutral Red (Cl. 50040); and the cyanine dye, Astrophloxine FF (C.I. 48070). Suitable dyes for selectively sensitizing the photoconductor to blue light include the yellow dye, 3-carboxymethyl-5-(3-ethyl-2(3)-benzothiazolylidene) rhodaninetriethylamine salt, the diphenylmethane dye Auramine (CI. 41000), the thiazole dye, Seto-Flavine-T (0.1. 49005), and the acridine dye Arcidine Yellow (CI. 46025).

The amount of sensitizing dye utilized is usually between about 0.00025 and about 0.25 weight percent based on the photoconductor. In general, the amount of sensitizing dye will depend upon the particular sensitizing dye, the coloring dye used in combination therewith, and the kind and type of photoconductor.

As previously discussed, in the azo system a color forming compound or coupler is included in the receptor. In

addition, as previously indicated, another chemical compound referred to as developer (either a developer base or a diazonium developer) is utilized to couple with the coupler to form the colored dye. The couplers or color forming compounds incorporated in the receptor for the azo system include phenols and fi-ketonic acid arylamides and other chemicals having reactive positions. For producing yellow the following couplers are included among the chemical compounds which may be utilized: benzoylacet-o-anisidide, benzoylacet-5'-chloro-o-anisidide, benzoyl acet-2',5-diethoxyanilide, acetoacet-o-anisidide, 3- methyll-phenyl-S-pyrazolone, terephthaloylbis (5 '-chloro- 2,4-dimethoxyacetanilide terephthaloylbis 4-chloro-2- methoxy-S'-chloroacetanilide), bisacetoacet-o-tolidide and Z-acetoacet 6 -ethoxybenzothiazole. The last four are designated respectively Naphtol ASLG, Naphtol AS L3G, Naphtol ASG and Naphtol ASL4G in Venkataraman, K., The Chemistry of Synthetic Dyes, Academic Press, Inc., New York, 1952, page 654. The following couplers comprise those useful for producing the color magenta: 2-naphthol, 6-brom0-2-naphthol, 6-chloro-2- naphthol, 6 acetamide'2-naphthol, 3-hydroxy-2-naphthamide, methyl 3-hydroxy-2-naphthoate, ethyl 3-hydroxy- 2-naphthoate, 3hydroxy-2-naphtha.nilide (this is designated Naphtol AS in Venkataraman, page 653), 3-hydroxy 2 naphthyl-3 nitroanilide (Naphtol ASBS, Venkataraman, page 653) and 3-hydroxy-2-naphthyl-5- chloro-2,4'-dimethoxyanilide (often referred to as Naphthol ASITR in its commercial form), 3-hydroxy- Z-naphthyl-o-toluidide (Naphtol ASD, Venkataraman, page 653) and many other so-called Naphtols of the 3-hydroxy-2-naphthylarylamide type. The couplers useful for producing the color cyan comprise: 3-hydroxy-2-anthrao -toluidide (Naphtol ASGR, Venkataraman, pages 652 and 653), and 2-hydroxy-a-benzocarbazole-3- carboxy-p-toluidide (Naphtol AS-SG Venkataraman, pages 652 and 653). The materials utilized in the development step to develop the colors of the couplers include developer bases which are primary aromatic amines, and the diazonium developers which are stable compounds such as diazoimino, diazoamino or diazosulfonate derivatives of the same diazotized aromatic amines, or are stabilized diazonium salt structures obtained from the aromatic amines. Among the aromatic amines which are used as such (followed by diazotization in situ) or in the form of stabilized derivatives of their diazotized forms are: 5-chloro-o-toluidine, N-phenyl-p-phenylenediamine, l-naphthylamine, 4-nitro-o-anisidine, 5-chloro-2-(4-chlorophenoxy) aniline, 5-chloro-o-anisidine, 4-methoxy-N butyl metanilarnide, 4-amine-2,5 dimethoxybenzonitrile, Z-nitrO-p-anisidine, 4-arnino-5'-'chloro-2' methoxybenzanilide, 4'-amino-2'5 dirnethoxybenzanilide, 4 amino- 2'5 diethoxybenzanilide, 4-benzamido-S-methyl-o-anisidine, 4-nitro-o-anisidine, 4-nitro-o-toluidine, 4-chloro-2- nitroaniline, 2-chloroaniline, 4-chloro-o-toluidine, 5-nitroo-anisidine, p-anisidine, 2,5-dimethoxy-p aminoacetanilide, 3-(p-arninophenoxy)phopionic acid, o-phenetidine, o-anisidine, p-phenetidine and 2,5-diethoxyaniline.

All of the above developers are suitable for incorporation with the coupler into the receptor sheet initially. In some cases a two color system is all that is required for reproduction purposes. In this instance yellow and magenta shades may be developed by using certain developers in the chemical development step of this invention. In other words in these instances the developer is not incorporated into the receptor sheet. Certain single developers are useful for bringing forth both the yellow and magenta shades and they include S chloro-o-toluidene and 5-chloro-o-anisidine. Where all three subtractive colors are to be developed simultaneously by the use of a single developer in the chemical development step the following developers have been found to be satisfactory: 4-amino- 2',5'-dimethoxy benzanilide, 4 amino 2',5 diethoxy benzanilide and 4'-amino-2',5-dibutoxy benzanilide.

The oxidation system utilized for producing the color also uses a coupler or color former incorporated in the receptor. The coupler is also developed by a developer used before or in conjunction with a water soluble oxidizing agent. Couplers for the oxidation system include certain phenols and active methylene containing compounds such as the fi-ketonic acid derivatives. Examples of suitable oxidation couplers for producing the color yellow include acetoacet-o-anisidide, acetoacetanilide, benzoylaceto-anisidide, benzoylacet--chloro o anisidide, benzoylacet-2',5'-diethoxyanilide, Naphtol AS-L4G, Naphtol AS- L3G, and 4-(tolylsulfonamido) benzoylacetanilide. Suitable couplers for producing the color magenta include 3-methyl-1-phenyl-5-pyrazolone, 2 cyanoacetylcoumarone, B-acetamido-l-phenyl-S-pyrazolone and 1-phenyl-3- (p-tolylcarbamyl)-5-pyrazolone. Suitable oxidation couplers for producing the color cyan include 2,4-dichloro-1- naphthol, l-hydroxy 2' dimethoxy 2 naphthanilide, 1-hydroxy-N-Z-naphthyl-Z-naphthamide, 2,6 dibromo- 1,5-dihydroxynaphthalene, 2 -chloro 6 phenylphenol, phenyl l-hydroxy-Z naph-thoate, 1 hydroxybenzanilide, and methyl 1-hydroxy-2-naphthoate. The developers used for developing the above couplers to produce the desired color on the exposed receptor include the primary amines such as the substituted and non-substituted para-dialkylaminoanilines. Examples of suitable developers of this type include: N ,N -diethyl-p-phenylenediamine, N ,N diethyl-3-methyl-p-phenylenediamine, N ,N dimethylp-phenylenediamine and N ,N -diethyl-3-methylsulfonylp-phenylenediamine. The water soluble oxidizing agents include both inorganic and organic materials such as potassium borate, sodium persulfate, ferric chloride, potas-' sium ferricyanide, calcium hypochlorite, potassium permanganate, sodium dichromate, sodium hypochlorite, benzoyl peroxide in alcohol solution and hydrogen peroxide. All the developers are useful when incorporated initially in the receptor with the coupler. A preferred single developer for simultaneously developing the three subtractive colors is N ,N -diethyl-p-phenylenediamine.

The color forming compounds or couplers are coated on the photoconductive receptor with the dispersion of the photoconductor in a pattern or mosaic as previously described. When not incorporated in the receptor with the coupler, the organic developers are coated over the surface on the exposed receptor during the chemical development step with an organic solvent such as methyl alcohol, ethyl alcohol or heptane. The use of the same organic solvent for dispersion of photoconductor and the coupler and the developer chemical used in the chemical development step aids in mixing the colors which have not been blocked out during the electrolytic development step of the process.

An amount of potential colorant between about 0.01 and about 0.2 weight percent based on photoconductor is satisfactory, the actual amount depending on the depth of color desired.

The dye sensitizers may be used singly or in combination of two or more dyes. The same applies to the couplers or color forming compounds and developers.

As previously mentioned, insulating resinou binders are utilized to bond the photoconductor particles together as well as to bind the resulting photoconductive layer to the supporting surface. The preferred resinous bonding agents are those which are no more conductive than the photoconductor under dark adapted conditions. The resinous binder should also preferably have a low degree of wettability toward the photoconductive particles as well as being substantially water insoluble so that the binder mainly collects in the interstices between particles and does not usually form a complete film around the photoconductive particles. Suitable binders include the copolymer of styrene and butadiene (in a Weight ratio of 70:30 to 85:15) known as Pliolite, polystyrene, chlorinated rubber (Parlon), polyvinylchloride, Saran (polyvinylidene chloride), nitrocellulose, and polyvinylbutyral. The weight ratios of binder to photoconductive particles 10 generally range from 1:10 to 1:1; preferably, 1:6 to 1:3.

In preparing the photoconductive layer, mixtures of two or more photoconductors may be utilized. Similarly, two or more binders may be used in admixture. Also, inert fillers or pigments, such as titanium dioxide and barium sulfate, may be admixed with the photoconductor and binder.

Quite generally, increasing amounts of scnsitiz'er (per unit weight photoconductor) increases the sensitivity, but it levels 013? beyond a certain point, presumably due to adsorption saturation and light-filtering action of the dye.

The following methods are useful in preparing various types of colored mosaics or patterns on the receptor in accordance with this invention. One method is the successive silk screening or spraying of three different color producing dispersions through a stencil which has a regular pattern of openings such that for each successive spraying operation the same stencil can be used in a slightly different position. The result is that the three dispersions are interlayed between each other without appreciable overlapping. These dispersions included the photoconductor, appropriate dyes, color forming chemicals, binder and a solvent. Etched metal foil stencils, such as copper, can also be used in place of a silk screen for this purpose.

A gravure-ty-pe printing plate having patterns similar to the stencil is useful in another method of forming the mosaic or pattern. The three patterns are interlayed on the same surface by transferring the three colored dispersions from the cavities in the plate.

Several methods employing the use of uniform coatings of essentially unsensitized particulate photoconductor, such as ZnO, have been found to be satisfactory for forming the mosaic. In one method, the sensitizing dyes and color forming chemicals in solution are wiped or sprayed through stencils in three successive interlaying steps onto a photoconductive coating, already laid down and bonded to the receptor. In another method, dark adapted ZnO coatings bonded to a suitable metal layer or support are exposed with light through photographic screens and the different sensitizer dyes and color forming chemicals laid down by electrolysis or electrostatic technique. Repeating the procedure three times with different color compositions, the interlayed pattern is produced. Also, the sensitizer dyes and color forming chemicals can be printed onto the photoconductive surface in an interlaying pattern by conventional gelatin duplicator technique or spirit duplicator, or other conventional printing processes such as gravure, letter press, and lithography.

Stripe or line patterns may be drawn by hand on metal and paper surfaces as repeating triplets of parallel lines of the three dispersions. Also, a sheet of rnetalized paper or metal foil may be wrapped around a cylinder and placed in a lathe. A motor-driven hypodermic syringe mounted on the lathe carriage ejects a small stream of photoconductor dispersion containing the appropriate dyes and chemicals onto the sheet on the cylinder While the lathe performs an operation similar to threading. A sufficiently large space is left between the lines to interlay the other colored dispersions as similar lines.

' Another method uses a rectangular block of metal having 50 or more fine grooves per inch milled almost across the entire surface of one side of the block. On the opposite surface of the block is out three reservoirs and at right angles to the fine grooves on the lower surface and of such depth that the first reservoir is connected to every third fine groove below; the second reservoir to every fine groove on one side of those that connected to the first reservoir; and the third reservoir connected to the remaining fine grooves. This grooved surface is laid on the sheet to be coated. On pouring the three color forming dispersions of the photoconductor and dyes into the three reservoirs, respectively, and moving a sheet of metal or metal- 11 ized paper parallel to the grooves, an interlayed striped mosaic coating is automatically produced.

In still another method, three color forming dispersions containing photoconductor, resin binder, chemical and dye can be made into the form of fine dry beads or balls. This is accomplished by separately spray drying the dispersions in a conventional manner to form beads of about 0.001 inch in diameter. The fine beads of different color forming properties are mixed. Metalized paper or metal foil is soaked or dampened with a solvent, such as toluene, and the damp substrate is then dipped into the dry beads and removed whereby a close packed adherent monolayer of beads is attached to the surface of the substrate. The beads should be softened by solvent and heat and then flattened by pressing into a smooth surface suitable for use in the electrolytic development.

If one of the photo-conductor dispersions is sprayed from a paint gun onto a metal surface using the technique of electrostatic spraying and the spraying is stopped when about one-third of the metal surface is covered with fine droplets of the dispersion, the spraying of the second dispersion will, under these conditions, place its droplets mostly between those already on the metal plate, and similarly with the third dispersion. Drying is carried out between spraying steps. In this way a random mosaic is created.

The electrolytic development technique must be performed with coatings on good conductors such as metals and without bare spots or pin holes where the metal is exposed and the particles of photoconductor should contact each other and the metal layer to assure a conductive path in light-struck areas. A thin gelatin layer or film may be placed over the mosaic pattern as a protective surface and as a means of aiding electrolytic development, especially when the gelatin layer contains an electrolyte.

The photoconductive receptor of this invention is suitable for reproduction of a color image by exposure of the receptor to a color radiation pattern or light image, usually of the three primary colors. As a result of exposure to the radiation pattern or light, a differentially conductive pattern is formed on the receptor surface by virtue of the increased conductivity of the photoconductor in the light-struck areas of the mosaic. The difference in conductivity of the fully irradiated areas as compared to the non-irradiated areas is at least times and generally as much as 100 times or greater.

The surface of the exposed receptor is then contacted in the dark or in subdued light with a solution containing an electrolyte and an electric potential is applied be tween the receptor and the electrolyte solution. The conductive layer, such as a metal layer, of the receptor is connected to source of direct current or grounded, and the electrolytic solution is connected to the opposite potential of the direct current. A voltage is impressed across the electrolytic solution and the conductive layer of the receptor while the receptor is in contact with a developer material which results in the reproduction of the image or pattern by deposition of resinous material on the conductive areas of the receptor. This may be done simultaneously with the exposure step, or as a subsequent step since the receptor sheet, particularly in the case of zinc oxide, has a useful memory of as much as several minutes. Suitable electrolytes include sodium chloride, sodium carbonate, sulfuric acid, acetic acid and sodium hydroxide.

The development may be carried out either anodically or cathodically, depending upon the type of photoconductor on the surface, the receptor construction, and the kind of resinous material used. In other words, the receptor may be connected to the positive or negative source of dire-ct current without departing from the scope of this invention.

In such electrolytic development, a suitable resinous material is dissolved or suspended in water and the surface of the receptor contacted with the aqueous electro- 112 lyte medium, such as by inserting the receptor in a vessel containing the aqueous medium or by brushing the aqueous medium on the surface with a sponge or gelatin roller or the like, which is connected to a direct current source.

An example of a suitable combination of developer material and aqueous electrolyte is an aqueous latex or suspension or emulsion containing negatively or positively charged polymer or resin particles containing a white pigment, such as titanium dioxide or zinc sulfide. Examples of solid polymers or resins which are positively charged in aqueous medium and, therefore, are useful as a component of an aqueous electrolyte solution when in suspension or emulsion for cathodic development include a polymer of a fatty acid and a polyamine (Versamid), a copolymer of vinyl chloride and vinyl acetate, polyvinyl acetate, silicones and epoxy resins. Examples of solid polymers or resins which are negatively charged in aqueous medium and, therefore, are useful as a component of an aqueous suspension or emulsion for anodic development include nylon, polyethylene, chlorinated rubber, polybutadiene, a copolymer of butadiene and styrene (Pliolite), and acrylic polymers and copolymers. Some of such polymers or resins may be suificiently white in color and opaque that an added white pigment is unnecessary. During electrolysis, the charged white particles are deposited selectively on the latent image or conductive pattern during electrolysis.

When using zinc oxide as the photoconductor, the receptor is usually made the cathode in the electrolytic process for best results because of the rectifying effect of the zinc oxide-electrolytic solution interface. With zinc oxide, a particularly useful developer material includes dissolved Versamid and suspended titanium dioxide in an aqueous electrolytic solution. Versamid 100 is a low molecular weight polymer of a fatty acid and a polyamine hydrochloride or polyamine polyhydrochloride which is soluble in water. It is semi-solid at room temperature, melts at 43 53 C. and has an amine value of 83-93. About 1 to 2 percent by weight of the Versamid is used in a dilute aqueous acid solution. About 1 to 10 percent by weight of titanium dioxide based on water is suspended in the solution. The particle size of the titanium dioxide is between 0.1 and 0.4 micron in average diameter but may exist as larger agglomerates in suspension. During electrolysis the light-struck areas of the receptor surface which are conductive become alkaline. The Versamid 100 will .precipitate in the alakaline areas of the receptor and the titanium dioxide will adhere to the precipitated Versamid 100 forming white areas.

In a modification of the electrolytic development step when using Zinc oxide as the photoconductor, the latent image is first cathodically developed using an aqueous electrolyte solution containing a soluble metal salt, such as silver nitrate or copper sulfate, whereby metal is electrolytically deposited in the light-struck areas which serve as the cathode. Thereafter, in a second development step, the developed receptor from the first development step is subjected to a second electrolytic development, but in this second development an anodic system is used in which the aqueous electrolyte solution contains negatively charged water-insoluble white polymer particles in suspension or in emulsion. The negatively charged particles deposit on the metal plated areas formed by the first development, which areas are now the anode of the system. In this manner, the normal rectifying effect of zinc oxide in an anodic system is overcome because of the metal surface on the zinc oxide formed in the first development step.

The current density necessary for development by electrolysis is usually between about 1 and about 100 milliamperes per square centimeter. In general, the voltage required to give such a current through the electrolytic solution and receptor is between about 3 and about 200 volts, usually between 10 to 60 volts per mil thickness of coating. The time required to produce the visible deposit of the developer material by electrolysis is between about 0.1 second and about 1 minute depending upon the current and the electrolyte and resin.

After the electrolytic development step the receptor is coated with a layer of White or pigmented resin in the areas which were sensitive to the particular colored light falling thereon. The receptor is dried and then it is coated again over the entire surface thereof with the developer chemicals which are suitable for the particular type of development to be carried out, e.g. azo system. The developer chemicals when not already incorporated in the receptor are dissolved usually in an organic solvent and swabbed over the surface. In the case of the azo system or the oxidation system two chemical development steps are required. One is the coating of the electrolytically blocked receptor with the organic developer in an organic solution. The receptor is then dried and an aqueous solution of a water soluble chemical is swabbed over the surface of the treated receptor or heat is used to bring forth the appropriate color. After this last step the receptor is dried and when viewed it is a faithful reproduction of the original colored negative.

The following examples are offered as a better understanding of the present invention and are not to be construed as unnecessarily limiting thereto.

Example 1 A suspension of the photoconductor and insulating resin was prepared by mixing 150 grams of a 30 percent solids toluene solution of Pliolite 5-7 (a copolymer of styrene and butadiene), 75 grams of a 30 percent toluene solution of polyvinyltoluene, 105 grams of Z-butanone, and 270 grams of zinc oxide (having a photoconductivity of at least lmho/cm.). The mixture was then blended in a Waring Blendor with the appropriate sensitizer dye and coupler.

The mixing in the Waring Blendor was accomplished by first adding the Pliolite and polyvinyltoluene solutions followed by adding the 2-butanone and stirring the mixture slowly. During the slow stirring, the zinc oxide was sifted in slowly into the vortex of the stirring mixture. After the entire mixture had been placed in the Waring Blendor, the blender was turned to high speed and stirred for at least minutes. The temperature of the mixture must be maintained below 160 F. during mixing. The mixture was then transferred to a ball mill and milled for at least 2 hours until the dispersion passed a 400 mesh screen. Thereafter, the proper selective color sensitizing dye and color forming chemical were added. In this case, to the above was added 20 grams of Z-butanone containing 1 gram of acetoacet-o-anisidide and 4 grams of a 0.3 percent solution in methanol of the blue light sensitizing dye 3-carbomethyl-5-(3-ethyl-2(3 -benzathiazolylidene) rhodanine triethanolamine salt to make the mixture responsive to blue light and a potential yellow color.

The above procedure was repeated for a second batch in which 20 grams of Z-butanone containing one gram of Z-naphthol and 4 grams of a 0.1 percent methanol solution of the green sensitizing dye Phloxine B were added to the initial zinc oxide mix containing the super sensitizer to make this batch sensitive to green light and capable of yielding a magenta color when developed with a suitable diazotized base. A third dispersion was prepared as above with 40 grams of 2-butanone containing one gram of Naphtol AS-GR and 4 grams of a 0.2 percent methanol solution of the red sensitizing dye Patent Blue V by adding to the initial mixture of zinc oxide and super sensitizer in accordance with the above procedure to sensitize the mixture to red light and make it a potential cyan color.

The dispersions were then ready for separate application to a base material or support. In this example, these dispersions were added as lines through a hypodermic syringe to aluminum foil rotating on a lathe. The first line was added at a rate of 2 feet per minute and dried at a temperature of 90 to 100 F. Similarly, the second and third lines of a different color were added so that the entire metal foil was completely covered with the three different colored lines. The aluminum foil should be clean and free of grease and dirt. In addition, it is preferred to wash the aluminum foil prior to depositing the mosaic thereon with an aqueous solution of potassium hydroxide to remove any aluminium oxide on the surface.

The above sheet was then dark adapted for about onehalf hour at 150 F. The completed receptor was then exposed for one second to a Kodachrome colored transparency projected thereon with a 300 Watt General Electric Projection Lamp. Thereafter, the sheet was connected to the negative electrode of a 50 volt direct current potential and placed in an electrotlytic solution containing 1 percent Versami'd (polyarnide resin) admixed with an epoxy resin and suspended titanium dioxide in an amount of about 3 weight percent based on water. The positive electrode of the DC source was connected to the electrolytic solution. Approximately 2 milliamps of current were passed three seconds whereby titanium dioxide and resin were deposited on the latent image. The receptor was then removed from the electrolytic solution and heated at about 200 F. to dry the receptor and fuse the deposited resin.

Then a solution of a developer comprising a 0.4 percent ethanol solution of 4amino-2,5-diethoxybenzanilide was applied by dipping. The solvent was allowed to evaporate.

A solution made from 200 parts water, 1 part sodium nitrite and 2 parts formic acid is now applied by dipping. In a short time, the background becomes colored whereas the imaged areas which have been blocked with the resin remain essentially white. A faithful reproduction of the colored original results.

Example 2 The procedures for preparation of the zinc oxide dispersions were the same as in Example 1. The yellow forming dispersion was the same as that used in Example 1. The procedure for preparation of the yellow forming dispersion was repeated for a second batch in which 25 grams of 2-butanone containing one gram of 2-cyanoacetylcoumarone and 5 grams of a 0.1 percent methanol solution of the green sensitizing dye Phloxine B were added to the initial zinc oxide mix containing the super sensitizer to make this batch sensitive to green light and capable of yielding a magenta color on subsequent chemical development. A third dispersion was prepared with 25 grams of Z-butanone containing one gram of 1- hydroxy-2'5-dimethoxy-Z-n-aphthanilide and 5 grams of a 0.2 percent methanol solution of the red sensitizing dye Patent Blue V by adding to the initial mixture of zinc oxide and super sensitizer in accordance with the above procedure to sensitize the mixture to red light and make it a potential cyan color. I

The dispersions were then ready for separate application to a base material or support. In this example, these dispersions were applied to the receptor in the manner described in Example 1.

The above sheet was then dark adapted and exposed also as in Example 1 and subsequently electrolytically developed as in Example 1.

Then a solution of a developer comprising one gram of N',N'-diethyl-p-phenylenediamine in 36 grams of heptane was applied by dipping. The solvent was allowed to evaporate.

A solution made from 25 grams water and 2 grams sodium persulfate was then applied by dipping. In a short time, the background became colored whereas the imaged areas which have been blocked with the resin remain essentially white. A faithful reproduction of the colored original results.

The oxidation reaction can be speeded, if desired, by warming the persulfate solution.

Having described my invention, I claim:

1. A method for making a colored reproduction of a colored image which comprises projecting a colored light image onto a receptor comprising a relatively non-conductive backing, a metal layer overlying and afiixed to said backing, and a photoconductive layer bonded to said metal layer to form the image receptive area comprising an admixture of a photoconductor and an insulating organic resinous binder, said photoconductive image receptive area being laterally divided into a pattern or mosaic of three different visually subtractive color forming areas, said three differentially subtractive colored areas separately containing at least one cyan forming coupler, at least one magenta forming coupler and at least one yellow forming coupler, and in addition separately containing at least one red-light sensitizing dye in said cyan forming area, at least one green-light sensitizing dye in the magenta color forming area, and at least one blue-light sensitizing dye in the yellow forming area, to form a differentially conductive pattern corresponding to said light image, subjecting said receptor containing the differentially conductive pattern to electrolysis in contact with an aqueous electrolytic solution containing a white pigment dispersed therein and a resin capable of depositing on the conductive areas of said receptor whereby the white pigment is aflixed to the conductive areas of said receptor masking the color thereunder, and subsequently chemically developing the couplers in the nonmasked color forming areas.

2. The process of claim 1 in which said couplers are developed to form an azo dye.

3. The process of claim 1 in which said couplers are developed by oxidation.

References Cited UNITED STATES PATENTS 2,939,787 6/1960 Giaimo 96l.3 3,212,887 10/1965 Miller et al. 96-1.7 3,226,307 12/1965 Tokumoto 961.2 3,245,785 4/1966 Miller et a1. 96-1 3,251,687 5/1966 Fohl et al. 96l.5 3,253,913 5/1966 Smith et a1. 96-1.2

NORMAN G. TORCHIN, Primary Examiner.

J. TRAVIS BROWN, Examiner.

C. E. VAN HORN, Assistant Examiner. 

1. A METHOD FOR MAKING A COLORED REPRODUCTION OF A COLORED IMAGE WHICH COMPRISES PROJECTING A COLORED LIGHT IMAGE ONTO A RECEPTOR COMPRISING A RELATIVELY NON-CONDUCTIVE BACKING, A METAL LAYER OVERLYING AND AFFIXED TO SAID BACKING, AND A PHOTOCONDUCTIVE LAYER BONDED TO SAID METAL LAYER TO FORM THE IMAGE RECEPTIVE AREA COMPRISING AN ADMIXTURE OF A PHOTOCONDUCTOR AND AN INSULATING ORGANIC RESINOUS BINDER, SAID PHOTOCONDUCTIVE IMAGE RECEPTIVE AREA BEING LATERALLY DIVIDED INTO A PATTERN OR MOSAIC OF THREE DIFFERENT VISUALLY SUBTRACTIVE COLOR FORMING AREAS, SAID THREE DIFFERENTIALLY SUBTRACTIVE COLORED AREAS SEPARATELY CONTAINING AT LEAST ONE CYAN FORMING COUPLER, AT LEAST ONE MAGENTA FORMING COUPLER AND AT LEAST ONE YELLOW FORMING COUPLER, AND IN ADDITION SEPARATELY CONTAINING AT LEAST ONE RED-LIGHT SENSITIZING DYE IN SAID CYAN FORMING AREA, AT LEAST ONE GREEN-LIGHT SENSITIZING DYE IN THE MAGENTA COLOR FORMING AREA, AND AT LEAST ONE BLUE-LIGHT SENSITIZING DYE IN THE YELLOW FORMING AREA, TO FORM A DIFFERENTIALLY CONDUCTIVE PATTERN CORRESPONDING TO SAID LIGHT IMAGE, SUBJECTING SAID RECEPTOR CONTAINING THE DIFFERENTIALLY CONDUCTIVE PATTERN TO ELECTROLYSIS IN CONTACT WITH AN AQUEOUS ELECTROLYTIC SOLUTION CONTAINING A WHITE PIGMENT DISPERSED THEREIN AND A RESIN CAPABLE OF DEPOSITING ON THE CONDUCTIVE AREAS OF SAID RECEPTOR WHEREBY THE WHITE PIGMENT IS AFFIXED TO THE CONDUCTIVE AREAS OF SAID RECEPTOR MASKING THE COLOR THEREUNDER, AND SUBSEQUENTLY CHEMICALLY DEVELOPING THE COMPLERS IN THE NONMASKED COLOR FORMING AREAS. 